stream_writers refactor broke compatibility with AUTO_START_UNSET and UnsetAutoStartSentinel #821
Description
<nidaqmx.stream_writers.UnsetAutoStartSentinel object> changed to <nidaqmx.stream_writers._channel_writer_base.UnsetAutoStartSentinel object>
This sounds like compatibility breakage. Previously, clients could import UnsetAutoStartSentinel and AUTO_START_UNSET, and now they can't.